Field of the Invention
The present invention relates to technology sending a command in a timely manner within an image forming apparatus.
Description of the Related Art
Scanning light is known to bend due to tilting of an optical system provided in an exposure unit of an image forming apparatus. Such bending can be corrected by creating profile data in advance, and driving a laser according to the profile data (see Japanese Patent Laid-Open No. 2009-126002, and Japanese Patent Laid-Open No. 2011-104959).
Incidentally, increased speed of an electrophotographic printer engine is realized by introducing multibeam exposure by a plurality of laser diodes. However, because respective control signals are necessary for the plurality of laser diodes, there is an increase in control signal lines and video signal lines. Consequently, it is conceivable to use a common line for a control signal line and a video signal line. This can be realized by connecting a video ASIC that outputs a video signal, and a PWM-IC that generates a PWM signal from a video signal that has been input and outputs the generated PWM signal to a laser driver (referred to below as an LD), in a high-speed serial communication scheme. The letters ASIC are an abbreviation for ‘application specific integrated circuit’. The letters PWM are an abbreviation for ‘pulse width modulation’. In a serial communication scheme, a video signal is sent in a period in which laser light is scanning an image area, and a control signal is sent in a period in which laser light is not scanning the image area. Thus, in a period corresponding to a non-image area, a laser power adjustment value, a shading correction amount, magnification information of a main scanning direction, or the like are transmitted as a control command. However, a plurality of control parameters such as a laser power adjustment value are each asynchronously calculated, loaded on a control command, and sent, so a serial communication scheme results in new problems. When a serial communication scheme and a multibeam light source are introduced, there are cases where send timing conflicts between a plurality of control commands. As a result, it is also conceivable that a control command arrives at the PWM-IC later than a timing when the control command is to be used in the PWM-IC. Therefore, it may not be possible for the PWM-IC to execute PWM control as intended.